Presentasi serupa

2 Electricity - The DangersAbout 5 workers are electrocuted every weeCauses 12% of young worker workplace deathsTakes very little electricity to cause harmSignificant risk of causing firesWhenever you work with power tools or electrical circuits there is a risk of electrical hazards, especially electrical shock. Risks are increased at construction sites because many jobs involve electric power tools.Electrical trades workers must pay special attention to electrical hazards because they work on electrical circuits. Coming in contact with an electrical voltage can cause current to flow through the body, resulting in electrical shock and burns. Serious injury or even death may occur.Electricity has long been recognized as a serious workplace hazard, exposing employees to electric shock, electrocution, burns, fires, and explosions. In 1999, for example, 278 workers died from electrocutions at work, accounting for almost 5 percent of all on-the-job fatalities that year, according to the Bureau of Labor Statistics. What makes these statistics more tragic is that most of these fatalities could have been easily avoided.OSHA Office of Training & Education

4 Electricity – How it WorksElectricity is the flow of energy from one place to anotherRequires a source of power: usually a generating stationA flow of electrons (current) travels through a conductorTravels in a closed circuitOperating an electric switch is like turning on a water faucet.Behind the faucet (or switch) there is a source of water (or electricity) with a way to transport it, and pressure to make it flow. The faucet’s water source is a reservoir or pumping station. A pump provides enough pressure for the water to travel through the pipes. For electricity the source is the power generating station. A generator provides the pressure (voltage) for the electrical current to travel through electric conductors (wires).Volts – the electrical pressure (measure of electrical force)Amps – the volume or intensity of the electrical flowWatts – the power consumedOSHA Office of Training & Education

5 OSHA Office of Training & EducationElectrical TermsCurrent -- electrical movement (measured in amps)Circuit -- complete path of the current Includes electricity source, a conductor, and the output device or load (such as a lamp, tool, or heater)Resistance -- restriction to electrical flowConductors – substances, like metals, with little resistance to electricity that allow electricity to flowGrounding – a conductive connection to the earth which acts as a protective measureInsulators -- substances with high resistance to electricity like glass, porcelain, plastic, and dry wood that prevent electricity from getting to unwanted areasResistance – Measured in ohms.Four factors determine the resistance of a material to the flow of electricity.What it is made of (silver is best, copper is most common)Its diameter (smaller diameter = more resistance)Its temperature (higher temperature = higher resistance)Its length (longer = higher resistance)OSHA Office of Training & Education

8 OSHA Office of Training & EducationElectrical InjuriesThere are four main types of electrical injuries:Direct:Electrocution or death due to electrical shockBurns / Flash: When heat from a nearby electrical arc causes thermal burns The temperature of an electrical arc can reach o CElectrical arcsIndirect - FallsContact electrical burns, 120-V alternating current nominal. The right knee was the energized side, and the left was ground.When an electrical shock enters the body it may produce different types of injuries. Electrocution results in internal and external injury to body parts or the entire body – often resulting in death. After receiving a “jolt” of electricity all or part of the body may be temporarily paralyzed and this may cause loss of grip or stability. A person may also involuntarily move as a result of receiving an electrical shock, resulting in a fall. Internal or external burns may result from contact with electricity.OSHA Office of Training & Education

11 OSHA Office of Training & EducationElectrical ShockAn electrical shock is received when electricalcurrent passes through the body.You will get an electrical shock if a part of yourbody completes an electrical circuit by…Touching a live wire and an electrical ground, orTouching a live wire and another wire at a different voltage.Electricity travels in closed circuits, and its normal route is through a conductor. Electric shock occurs when the body becomes a part of the circuit.Grounding is a physical connection to the earth, which is at zero volts.The metal parts of electric tools and machines may become energized if there is a break in the insulation of the tool or machine wiring. A worker using these tools and machines is made less vulnerable to electric shock when there is a low-resistance path from the metallic case of the tool or machine to the ground. This is done through the use of an equipment grounding conductor—a low-resistance wire that causes the unwanted current to pass directly to the ground, thereby greatly reducing the amount of current passing through the body of the person in contact with the tool or machine.OSHA Office of Training & Education

12 OSHA Office of Training & EducationShock SeveritySeverity of the shock depends on:Path of current through the bodyAmount of current flowing through the body (amps)Duration of the shocking current through the body,LOW VOLTAGE DOES NOT MEAN LOW HAZARDOther factors that may affect the severity of the shock are:- The voltage of the current.- The presence of moisture- The general health of the person prior to the shock.Low voltages can be extremely dangerous because, all other factors being equal, the degree of injury increases the longer the body is in contact with the circuit.The resistance of the body varies based on:The amount of moisture on the skin (less moisture = more resistance)The size of the area of contact (smaller area = more resistance)The pressure applied to the contact point (less pressure = more resistance)Muscular structure (less muscle = less resistance)OSHA Office of Training & Education

13 Dangers of Electrical ShockCurrents above 10 mA* can paralyze or “freeze” muscles.Currents more than 75 mA can cause ineffective heartbeat -- death will occur in a few minutes unless a defibrillator is useda small power drill uses 30 times as muchFor example, 1/10 of an ampere (amp) of electricity going through the body for just 2 seconds is enough to cause death.Currents above 10 mA can paralyze or “freeze” muscles. When this “freezing” happens, a person is no longer able to release a tool, wire, or other object. In fact, the electrified object may be held even more tightly, resulting in longer exposure to the shocking current. For this reason, hand-held tools that give a shock can be very dangerous. If you can’t let go of the tool, current continues through your body for a longer time, which can lead to respiratory paralysis (the muscles that control breathing cannot move). You stop breathing for a period of time. People have stopped breathing when shocked with currents from voltages as low as 49 volts. Usually, it takes about 30 mA of current to cause respiratory paralysis.Defibrillator in use* mA = milliampere = 1/1,000 of an ampereOSHA Office of Training & Education

16 OSHA Office of Training & EducationFallsElectric shock can also cause indirect injuriesWorkers in elevated locations who experience a shock may fall, resulting in serious injury or deathOSHA Office of Training & Education

17 Electrical Hazards and How to Control ThemElectrical accidents are caused by a combination of three factors:Unsafe equipment and/or installation,Workplaces made unsafe by the environment, andUnsafe work practices.Electrical shocks, fires, or falls result from these hazards:Exposed electrical partsOverhead power linesInadequate wiringDefective insulationImproper groundingOverloaded circuitsWet conditionsDamaged tools and equipmentOSHA Office of Training & Education

20 Control – Isolate Electrical Parts - Cabinets, Boxes & FittingsReference (b)(1)Conductors entering boxes, cabinets, or fittings. Conductors entering boxes, cabinets, or fittings shall be protected from abrasion, and openings through which conductors enter shall be effectively closed. Unused openings in cabinets, boxes, and fittings shall also be effectively closed.Covers and canopies. All pull boxes, junction boxes, and fittings shall be provided with covers. If metal covers are used, they shall be grounded. In energized installations each outlet box shall have a cover, faceplate, or fixture canopy. Covers of outlet boxes having holes through which flexible cord pendants pass shall be provided with bushings designed for the purpose or shall have smooth, well‑rounded surfaces on which the cords may bear.Conductors going into them must be protected, and unused openings must be closedOSHA Office of Training & Education

21 Control – Close OpeningsJunction boxes, pull boxes and fittings must have approved coversUnused openings in cabinets, boxes and fittings must be closed (no missing knockouts)Photo shows violationsof these two requirementsOSHA Office of Training & Education

23 Control - Overhead Power LinesStay at least 10 feet awayPost warning signsAssume that lines are energizedUse wood or fiberglass ladders, not metalPower line workers need special training(a)How Do I Avoid Hazards?-- Look for overhead power lines and buried power line indicators. Post warning signs.-- Contact utilities for buried power line locations.-- Stay at least 10 feet away from overhead power lines.-- Unless you know otherwise, assume that overhead lines are energized.-- Get the owner or operator of the lines to de-energize and ground lines when working near them.-- Other protective measures include guarding or insulating the lines.-- Use non-conductive wood or fiberglass ladders when working near power lines.OSHA Office of Training & Education

24 Hazard - Inadequate WiringHazard - wire too small for the currentExample - portable tool with an extension cord that has a wire too small for the toolWire GaugeWIREAn electrical hazard exists when the wire is too small a gauge for thecurrent it will carry. Normally, the circuit breaker in a circuit ismatched to the wire size. However, in older wiring, branch lines topermanent ceiling light fixtures could be wired with a smaller gaugethan the supply cable.Note that wire-gauge size is inversely related to the diameter of the wire. For example, a No. 12 flexible cord has a larger diameter wire than a No. 14 flexible cord.Choose a wire size that can handle the total current. Remember: The larger the gauge number, the smaller the wire!American Wire Gauge (AWG)Wire size Handles up to#10 AWG 30 amps#12 AWG 25 amps#14 AWG 18 amps#16 AWG 13 ampsWire gauge measures wires ranging in size from number 36 to 0 American wire gauge (AWG)OSHA Office of Training & Education

27 Control – Use the Correct WireWire used depends on operation, building materials, electrical load, and environmental factorsUse fixed cords rather than flexible cordsUse the correct extension cord(a)(2)(ii)(J)The OSHA standard requires flexible cords to be rated for hard or extra-hard usage. These ratings are to be indelibly marked approximately every foot of the cord. Since deterioration occurs more rapidly in cords which are not rugged enough for construction conditions, the National Electric Code and OSHA have specified the types of cords to use in a construction environment. This rule designates the types of cords that must be used for various applications including portable tools, appliances, temporary and portable lights. The cords are designated HARD and EXTRA HARD SERVICE.Examples of HARD SERVICE designation types include S, ST, SO, STO, SJ, SJO, SJT, & SJTO. Extension cords must be durably marked as per (g)(2)(ii) with one of the HARD or EXTRA HARD SERVICE designation letters, size and number of conductors.Must be 3-wire type and designed for hard or extra-hard useOSHA Office of Training & Education

28 Hazard – Defective Cords & WiresPlastic or rubber covering is missingDamaged extension cords & toolsExtension cords may have damaged insulation. Sometimes the insulation inside an electrical tool or appliance is damaged. When insulation is damaged, exposed metal parts may become energized if a live wire inside touches them. Electric hand tools that are old, damaged, or misused may have damaged insulation inside. If you touch damaged power tools or other equipment, you will receive a shock. You are more likely to receive a shock if the tool is not grounded or double-insulated.OSHA Office of Training & Education

29 OSHA Office of Training & EducationHazard – Damaged CordsCords can be damaged by:AgingDoor or window edgesStaples or fasteningsAbrasion from adjacent materialsActivity in the areaImproper use can cause shocks, burns or fireReference (a)(2)(ii)(I)The normal wear and tear on extension and flexible cords at your site can loosen or expose wires, creating hazardous conditions. Cords that are not 3-wire type, not designed for hard-usage, or that have been modified, increase your risk of contacting electrical current.OSHA Office of Training & Education

30 OSHA Office of Training & EducationControl – Cords & WiresInsulate live wiresCheck before useInsulation is the most common manner of guarding electrical energy.Extension cords must be 3-wire type so they may be grounded, and to permit grounding of any tools or equipment connected to them.Extension cords when exposed to "normal" construction use can experience rapid deterioration. When this happens, conductors with energized bare wires can be exposed. Conductors can break or come loose from their terminal screws, specifically the equipment grounding conductor. If that occurs, the equipment grounding for the tool in use is lost.OSHA Office of Training & Education

31 OSHA Office of Training & EducationGroundingGrounding creates a low-resistance path from a tool to the earth to disperse unwanted current.When a short or lightning occurs, energy flows to the ground, protecting you from electrical shock, injury and death.Grounding is a secondary method of preventing electrical shock.Grounded electrical systems are usually connected to a grounding rod that is placed 6-8 feet deep into the earth.Grounded - connected to earth or to some conducting body that serves in place of the earth.Grounded, effectively (Over 600 volts, nominal.) Permanently connected to earth through a ground connection of sufficiently low impedance and having sufficient ampacity that ground fault current which may occur cannot build up to voltages dangerous to personnel.Grounded conductor. A system or circuit conductor that is intentionally grounded.Grounding conductor. A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.OSHA Office of Training & Education

32 Hazard – Overloaded CircuitsHazards may result from:Too many devices plugged into a circuit, causing heated wires and possibly a fireDamaged tools overheatingLack of overcurrent protectionWire insulation melting, which may cause arcing and a fire in the area where the overload exists, even inside a wallIf the circuit breakers or fuses are too big (high current rating) for the wires they are supposed to protect, an overload in the circuit will not be detected and the current will not be shut off. A circuit with improper overcurrent protection devices – or one with no overcurrent protection devices at all – is a hazard.OSHA Office of Training & Education

33 Control - Electrical Protective DevicesAutomatically opens circuit if excess current from overload or ground-fault is detected – shutting off electricityIncludes GFCI’s, fuses, and circuit breakersFuses and circuit breakers are overcurrent devices. When too much current:Fuses meltCircuit breakers trip openTo prevent too much current in a circuit, a circuit breaker or fuse is placed in the circuit. If there is too much current in the circuit, the breaker “trips” and opens like a switch. If an overloaded circuit is equipped with a fuse, an internal part of the fuse melts, opening the circuit. Both breakers and fuses do the same thing: open the circuit to shut off the electrical currentThe basic idea of an overcurrent device is to make a weak link in the circuit. In the case of a fuse, the fuse is destroyed before another part of the system is destroyed. In the case of a circuit breaker, a set of contacts opens the circuit. Unlike a fuse, a circuit breaker can be re-used by re-closing the contacts. Fuses and circuit breakers are designed to protect equipment and facilities, and in so doing, they also provide considerable protection against shock in most situations. However, the only electrical protective device whose sole purpose is to protect people is the ground-fault circuit-interrupter.OSHA Office of Training & Education

34 Power Tool RequirementsHave a three-wire cord with ground plugged into a grounded receptacle, orBe double insulated, orBe powered by a low-voltage isolation transformerCommon Examples of Misused Equipment = OSHA Violations* Using multi-receptacle boxes designed to be mounted by fitting them with a power cord and placing them on the floor.* Fabricating extension cords with ROMEX® wire.* Using equipment outdoors that is labeled for use only in dry, indoor locations.* Attaching ungrounded, two-prong adapter plugs to three-prong cords and tools.* Using circuit breakers or fuses with the wrong rating for over-current protection, e.g. using a 30-amp breaker in a system with 15- or 20-amp receptacles. Protection is lost because it will not trip when the system's load has been exceeded.* Using modified cords or tools, e.g., removing ground prongs, face plates, insulation, etc.* Using cords or tools with worn insulation or exposed wires.OSHA Office of Training & Education

35 Preventing Electrical Hazards - ToolsInspect tools before useUse the right tool correctlyProtect your toolsUse double insulated tools* Use tools and equipment according to the instructions included in their listing, labeling or certification.* Visually inspect all electrical equipment before use. Remove from service any equipment with frayed cords, missing ground prongs, cracked tool casings, etc. Apply a warning tag to any defective tool and do not use it until the problem has been corrected.Double Insulated markingOSHA Office of Training & Education

36 Clues that Electrical Hazards ExistTripped circuit breakers or blown fusesWarm tools, wires, cords, connections, or junction boxesGFCI that shuts off a circuitWorn or frayed insulation around wire or connectionThere are “clues” that electrical hazards exist. For example, if a GFCI keeps tripping while you are using a power tool, there is a problem. Don’t keep resetting the GFCI and continue to work. You must evaluate the “clue” and decide what action should be taken to control the hazard.There are a number of other conditions that indicate a hazard.Tripped circuit breakers and blown fuses show that too much current is flowing in a circuit. This could be due to several factors, such as malfunctioning equipment or a short between conductors. You need to determine the cause in order to control the hazard.An electrical tool, appliance, wire, or connection that feels warm may indicate too much current in the circuit or equipment. You need to evaluate the situation and determine your risk.An extension cord that feels warm may indicate too much current for the wire size of the cord. You must decide when action needs to be taken.A cable, fuse box, or junction box that feels warm may indicate too much current in the circuits.A burning odor may indicate overheated insulation.Worn, frayed, or damaged insulation around any wire or other conductor is an electrical hazard because the conductors could be exposed. Contact with an exposed wire could cause a shock. Damaged insulation could cause a short, leading to arcing or a fire. Inspect all insulation for scrapes and breaks. You need to evaluate the seriousness of any damage you find and decide how to deal with the hazard.A GFCI that trips indicates there is current leakage from the circuit First, you must decide the probable cause of the leakage by recognizing any contributing hazards. Then, you must decide what action needs to be taken.OSHA Office of Training & Education

37 Safety-Related Work PracticesTo protect workers from electrical shock:Use barriers and guards to prevent passage through areas of exposed energized equipmentPre-plan work, post hazard warnings and use protective measuresKeep working spaces and walkways clear of cords,Employees must not work near any part of an electric power circuit that the employee could contact in the course of work, unless the employee is protected against electric shock by de-energizing the circuit and grounding it or by guarding it effectively by insulation or other means.* In work areas where the exact location of underground electric power lines is unknown, employees using jack‑hammers, bars, or other hand tools which may contact a line shall be provided with insulated protective gloves.* Before work is begun, inquire or observe by instruments whether any part of an energized electric power circuit is so located that the performance of the work may bring any person, tool, or machine into physical or electrical contact with the electric power circuit. Post and maintain proper warning signs where such a circuit exists. The employer shall advise employees of the location of such lines, the hazards involved, and the protective measures to be taken.OSHA Office of Training & Education

38 Safety-Related Work PracticesUse special insulated tools when working on fuses with energized terminalsDon’t use worn or frayed cords and cablesDon’t fasten extension cords with staples, hang from nails, or suspend by wire.,Only qualified persons may work on electric circuit parts or equipment that have not been deenergized. Such persons shall be capable of working safely on energized circuits and shall be familiar with the proper use of special precautionary techniques, PPE, insulating and shielding materials, and insulated tools.Deenergize live parts that an employee may be exposed to before the employee works on or near them, unless the employer can demonstrate that deenergizing introduces additional or increased hazards or is infeasible due to equipment design or operational limitations. Live parts that operate at less than 50 volts to ground need not be deenergized if there will be no increased exposure to electrical burns or to explosion due to electric arcs.If the exposed live parts are not deenergized other safety-related work practices shall be used to protect employees who may be exposed to the electrical hazards. Employees must be protected against contact with energized circuit parts with any part of their body or indirectly through some other conductive object.Lock or tag out (or both) the circuits energizing the parts while any employee is exposed to contact with parts of fixed electric equipment or circuits which have been deenergized.If working near overhead lines, the lines shall be deenergized and grounded, or other protective measures shall be provided before work is started.Portable cord and plug connected equipment and extension cords shall be visually inspected before use on any shift for external defects (such as loose parts, deformed and missing pins, or damage to outer jacket or insulation) and for evidence of possible internal damage (such as pinched or crushed outer jacket).OSHA Office of Training & Education

39 Preventing Electrical Hazards - PlanningPlan your work with othersPlan to avoid fallsPlan to lock-out and tag-out equipmentRemove jewelryAvoid wet conditions and overhead power linesMake your environment safer by doing the following:Lock and tag out circuits and machines.Prevent overloaded wiring by using the right size and type of wire.Prevent exposure to live electrical parts by isolating them.Prevent exposure to live wires and parts by using insulation.Prevent shocking currents from electrical systems and tools by grounding them.Prevent shocking currents by using GFCI’s.Prevent too much current in circuits by using overcurrent protection devices.OSHA Office of Training & Education

40 OSHA Office of Training & EducationAvoid Wet ConditionsIf you touch a live wire or other electrical component while standing in even a small puddle of water you’ll get a shock.Damaged insulation, equipment, or tools can expose you to live electrical parts.Improperly grounded metal switch plates & ceiling lights are especially hazardous in wet conditions.Wet clothing, high humidity, and perspiration increase your chances of being electrocuted.A damaged tool may not be grounded properly, so the housing of the tool may be energized, causing you to receive a shock.Improperly grounded metal switch plates and ceiling lights are especially hazardous in wet conditions. If you touch a live electrical component with an uninsulated hand tool, you are more likely to receive a shock when standing in water. But remember: you don’t have to be standing in water to be electrocuted. Wet clothing, high humidity, and perspiration also increase your chances of being electrocuted.Use extra caution when working with electricity when water is present in the environment or on the skin. Pure water is a poor conductor, but small amounts of impurities, like salt and acid (both are in perspiration), make it a ready conductor.OSHA Office of Training & Education

41 Preventing Electrical Hazards - PPEProper foot protection (not tennis shoes)Rubber insulating gloves, hoods, sleeves, matting, and blanketsHard hat (insulated - nonconductive)Personal protective equipment (PPE) should always be the last line of defense against a hazard. If the hazard is unavoidable, and cannot be addressed in any other safe manner, then employees must be fitted with proper PPE.Safety shoes should be nonconductive and protect your feet from completing an electrical circuit to ground. They can also protect against open circuits of up to 600 volts in dry conditions. These shoes should be used with other insulating equipment and in connection with active precautions to reduce or eliminate the potential for providing a path for hazardous electrical energy.When it is necessary to handle or come close to wires with a potential live electrical charge, it is essential to use proper insulating PPE to protect employees from contact with the hazardous electrical energy.Specific types of hard hats are needed when performing electrical work.A “Class B” Electrical/Utility type hard hat protects against falling objects and high-voltage shock and burns.OSHA Office of Training & Education

42 OSHA Office of Training & EducationSummaryElectrical equipment must be:Listed and labeledFree from hazardsUsed in the proper mannerIf you use electrical tools you must be:Protected from electrical shockProvided necessary safety equipmentOSHA Office of Training & Education